Arc tube system



21, 1940- J. w. DAWSON 2,201,966

' ARC TUBE SYSTEM Filed July 14, 1959 LmE VOLTAGE c /LoAD CURRENT VOLTAGE AcRoss TUBES ZERO c AXIS 'F Hc. 3.

I INVENTOR. V "652 59355 JOHN W. DAwsoN,

ZERo' AXIS Patented May 21,1940

U ITED STATES PATENT OFFICE ARC TUBE SYSTEM John W. Dawson, Auburndale, Mass assignor to Raytheon Manufacturing Company, Newton, Man, a corporation of Delaware Application July 14, 1939, Serial No. 284,502

18 Claims.

This invention relates to an arc tube system, and more particularly to such a system in which two controlled arc tubes are connected inversely in order to supply a controlled alternating current load, such as a resistance welding load.

One of the principal objects of this invention is to devise a simple and reliable firing circuit for such are tubes.

Particularly when using igniting electrodes of the type which are separated from a cool cathode by an insulating wall, it is desirable to impress substantially only positive impulses on the igniting electrode, as described and claimed in my oopending application, Serial No. 254,203, filed February 2, 1939, for an improvement in Arc discharge starting arrangement and method.

Another object of this invention is to accomplish the above result in a simple and reliable manner.

In alternating current systems of this general nature, particularly in the case of resistance welding loads, it is desirable that if one of the arc tubes fails to conduct current upon the application of an igniting impulse to its igniting electrode, the other are tube shall also be prevented from starting. If this is not done, the current supplied to the load has a substantially direct current component which is usually disadvantageous.

A further object of this invention is to devise means responsive to the absence of conduction in either tube for deenergizing the firing circuit of the other tube.

The foregoing and other objects of this invention will be best understood from the following description of an exemplification thereof, reference being had to the accompanying drawing wherein:

Fig. 1 is a diagrammatic representation of a circuit embodying the present invention; and

Figs. 2 and 3 are curves illustrating the operation of the system shown in Fig. 1.

The embodiment illustrated consists of two are tubes 1 and 2 preferably of the mercury pool cathode type. These tubes contain mercury pool cathodes 3 and l, and anodes 5 and 6, respectively, and are provided with igniting electrodes 1 and 8. Although these igniting electrodes may be of any type which initiate an are on the mercury pool cathode by means of an igniting impulse supplied thereto, they preferably are of the type which consists of a conductor separated from the mercury pool by an insulating layer which preferably consists of glass. More particularly these igniting electrodes may be of the form described and claimed in the copending application of Percy L. Spencer, Serial No. 259,355, filed March 2, 1939, for an improveinent in Are starting devices. In igniting electrodes of this kind, the glass layer on the igniting elec- 5 trode conductor is in contact with the surface of the mercury pool, and the arc tends to form at some such point of contact. The upper ends of the electrodes 1 and 8 may be left exposed to the discharge so as to provide discharge paths in parallel with the respective cathodes and igniting electrodes. 7

Two alternating current lines 9 and iii are connected to supply a suitable alternating current load which may consist of a transformer 15 ll having a primary H, a secondary I3, and a load It. In the particular system shown, the load It may consist of a resistance welding load. The arc tubes I and 2 are interposed in one of the conductors ill in order to control the flow of current to the load. In order to permit alternating current to flow through the tube system,

' the two tubes are reversely connected by means of the crossed conductors l5 and i6. If the tubes 1 and 2 are conducting, current pulses of 5 one polarity will flow through tube l, and current pulses of the opposite polarity will flow through tube 2, thus delivering alternating current to the load. If, however, tubes l and 2 are non-conducting, the load is deenergized.

Igniting transformers ll and i8 are provided to supply igniting impulses to the igniting electrodes l and B, respectively. These igniting transformers are provided with secondary windings l9 and 20. The secondarywinding i9 is 35 connected between the igniting electrode l and the cathode pool 3, while the secondary winding 20 is connected between the igniting electrode 8 and the cathode pool 4. Thetransformers H and ii! are also provided with primary windings 2| and 22 which are supplied with igniting voltage impulses through a control circuit which is energized from a transformer 23 having a primary winding 24 connected directly across the tubes i and 2. For this purpose the two ends of the primarywinding 24 are connected respectively to the two conductors l5 and i6. The transformer 23 also has a secondary winding 25 which is connected to the primary winding 2i through a rectifier 26, and to the primary winding 22 through a rectifier 21. The rectifiers 28 and 21 are preferably of the copper oxide type. A- conductor 28 connects the point intermediate the rectifier 26 and the primary winding M to the point intermediate the primary winding 22 and the rectifier 2V.

Interposed in the connections leading from the secondary winding 25 is a pair of control contacts 29. These control contacts may be operated from a control pushbutton or from some suitable timing arrangement. Connected in series with the control contacts 2Q in the connectlon leading from the secondary winding 25 is a pair of contacts which are normally closed by means or a contact arm Elli. This contact arm Eiil may be opened by a relay 3i having an actuating coil 32 connected from one side of the secondary winding 25 to the lower of the two contacts Connected directly across the tubes 0 and 2 is a series circuit consisting of a resistance and a condenser 35. This circuit is to enable the incipient arc spots initiated by the igniting impulses supplied to the igniting electrodes l and ii ages involved. However, they do represent in a general qualitative manner the operation of the system. In Fig. 2 the sine wave or represents the line voltage Which appears across the conductors 9 and ill. The curve 1) represents the load current flowing to the primary winding it. In the systems which are contemplated, particularly resistance welding systems, the current I) lags the voltage a, and in the particular instance all said tubes.

shown, this lag is about degrees. As the current passes through zero, one of the arc tubes l or 2 goes out, and it is desirable that the other tube start immediately in order to deliver smooth alternating current to the load. The curve 0, which represents the voltage across the tubes l and 2, shows that when one of the arc tubes goes out, the voltage across said tubes rises very rapidly to the instantaneous value of the line voltage at that particular moment. The system is so arranged that this voltage impulse is transmitted through the firing circuit so as to ignite the previously idle tube, which thereupon immediately starts conducting current so that the voltage across the tube then drops to the relatively low value of the arc tube drop. This operation takes such a short time that the rise in voltage across the tubes lasts for a very short time, and therefore these voltage impulses are represented in curve 0 by vertical lines. Of course it is to be understood that this change does occupy some time interval which, however, it is impractical to illustrate in Fig. 2. It will be seen, therefore, that the voltage across the tubes l and 2 supplies voltage impulses at exactly the right moment in order to alternately fire the tubes l and 2 so as to cause the alternating load current I) to flow smoothly through The primary winding 26 which is connected directly across the tubes l and 2 has this voltage wave 0 impressed upon it. This same voltage wave 0 is therefore impressed through the secondary winding 25 upon each of the primary windings 2i and 22 connected in series with their respective rectifiers 2t and 2?. The rectifier it permits the voltage impulses of aaoreoo a one polarity to pass through the primary winding 20, while the rectifier 271 permits voltage impulses of the opposite polarity to pass through primary winding 22.

The manner in which the control circuit network affects the voltages supplied thereto will be described in connection with Fig. 3. The curve d represents the voltage appearing in one of the secondary windings of the igniting transformers, for example secondary winding l9, and therefore represents the igniting voltage impressed between the igniting voltage U and the mercury pool cathode ii. If we assume that the rectifier 26 passes those impulses of the curve 0 which extend above the zero axis, we see that the voltage d appearing in the secondary winding til, which is also substantially the voltage across the primary winding 20, has substantially the same shape as the curve 0 for as long as said curve 0 extends above the zero axis. As the curve 0 tends to reverse, the rectifier 26 stops conducting current. However, at this time current is flowing through the primary winding 2i, and if this current were suddenly stopped, a relatively large back voltage would be induced in the primary winding 2i, and therefore in the secondary winding is which would supply a voltage impulse to the igniting electrode l in the opposite direction to that of the main igniting impulse. The polarities of the various windings are so chosen that this main igniting impulse represented by the vertical portions of curve d makes the igniting electrode ll pom'tive with respect to its associated pool cathode 3. If, however, voltage impulses of the opposite polarity Were permitted to be supplied to the igniting electrode l, the disadvantages described in my copending application referred to above would exist. The system which I have illustrated, however, eliminates such reverse potential impulses. Upon cessation of conduction of the rectifier 253, the current which tends to persist in its flowing through the primary winding 26 has provided for it a low resistance path, consisting of the rectifier 2i and the conductor 28, through which said current may continue to flow. It will be seen that the direction of conduction of the rectifier 2V is such as to permit this to occur. Therefore, the current through the primary 2i continues to flow for a suiiicient period of time so that the flux through the transformer ll may gradually die down without inducing substantial voltages in said transformer. A slight reverse potential, as represented by the loop e in Fig. 3, does occur. However, the value of this voltage as well as the horizontal value of the voltage above zero axis is greatly exaggerated as compared with the vertical portions of curve d. In practice the vertical portions are of the order of several thousand volts while the horizontal portion in the loop e represents voltages of the order of several volts. We see, therefore, that in so far as the voltage impulses supplied to the igniting electrode 7] are concerned, they are substantially only positive impulses.

The analysis given above in connection with igniting electrode ll applies with equal force to igniting electrode ii. The only difference is that in the case of the igniting electrode 8, the rectifier 2'1? picks out those impulses of the curve 0 represented in Fig. 2 as extending below the zero axis. In this case likewise, the polarities are so chosen that the substantial unidirectional voltage impulses supplied to the electrode d are positive.

Eli

'previously described, are of such short duration It will be noted that in the present instance even the relatively small horizontal voltage of the curve d above the zero axis is positive throughout the conduction of current in its associated tube. As pointed out in my copending application, it is advantageous that whatever voltages exist on the igniting electrode shall be positive as long as any substantial conduction of current occurs in the associated tube. In this way positive ion bombardment of the insulator surrounding the conductor of the igniting electrode, which tends to make said insulating surface insensitive, is substantially prevented.

when the control contacts 29 are closed at the point where the vertical portion of curve would normally occur, the igniting circuit is energized and the tubes l and 2 conduct current substantially as described above. If, however, the control contacts 29 are closed earlier than said point as, for example, the zero point of the line voltage wave, the voltage on each igniting electrode will rise in accordance with a sine wave variation until a sufficient voltage is impressed on said electrode to cause ignition to occur. By adjusting the ratio of transformation of each igniting transformer I1 and IS, the requisite igniting voltage can be caused to occur substantially at the normal firing point of said tube, namely the point at which the load current would normally start from a zero value. An exact adjustment of this firing point is not essential, and I prefer to have the initial firing point occur somewhat earlier. Such delayed firing beyond the zero point of the line voltage tends to make the initial flow of current coincide more closely with the normal current flow, and thus tends to eliminate transients.

The operation as described above provides an 1 inherent protection for the igniting electrodes against application thereto of excessive voltages. During any operation of the system, the voltage applied to the ignitingelectrode will rise until that voltage is sufficient to cause ignition. At that instant the initiation of conduction in the associated tube causes the voltage across that tube to drop to the relatively low value of the arc drop. This effectively removes the voltage supplied to the igniting electrode. 'I'herefore the system operates inherently so that the voltage supplied to each igniting electrode is never greater than that necessary to effect ignition. By adjusting the ratio of transformation of the igniting transformers so as to initially tend to cause the igniting electrodes to fire somewhat before the vertical portions of the curve 0, as indicated above, at said vertical portions there is an excess igniting voltage available, if due to any reason a tube does not always fire at the minimum igniting voltage. Such variation in the required igniting voltage may be due to a number of causes; for example, variations in the level of the mercury pool with respect to the igniting electrode structure.

If one of the tubes l or 2 fails to become conducting upon an igniting impulse being supplied to its associated igniting electrode I or 8, the relay 31 operates to deenergize the igniting circuits of both tubes. This may be described in connection with the curves shown'in Fig. 2. It will be seen that during normal operation of the system, the voltage which is impressed upon the operating coil 32 of the relay 3| is represented by the curve 0. The only portions which have any substantial magnitude are the vertical portions of this curve. However, these vertical portions, as

that they are insuiilcient to cause the coil 22 to operate the relay 3|. If, however, upon the occurrence of an igniting impulse at one of the igniting electrodes, the associated tube does not become conducting, the voltage across the tubes, instead of falling to the relatively low value represented by the voltage drop of the tube, continues to follow the line voltage 0. Therefore, upon the failure of a tube to become conducting, coil 32 is supplied with a considerable voltage which persists throughout the remaining portion of the voltage wave. The relay ii is so designed that this voltage is sufilcient to cause the coil 32 to operate the relay 3i. When the relay Si is operated, the contact arm II opens its associated contacts, and thereafter no impulses are supplied to the igniting transformers l1 and i8. There-- fore neither of the tubes I and 2 are permitted to fire. Under these conditions the voltage across the tubes, instead of following the curve 0, is sub-- stantially the line voltage as represented by the curve a. Under these conditions the coil 32 is continuously supplied with alternating current which is sufficient to keep the relay 3| in its operated-position. In order to restart the system,

the contacts 29 must be opened. In ordinary resistance welding operations, the contacts 28 are periodically opened and closed in order to produce successive welding operations. Thus upon the failure of any one tube to start, the system will be deenergized throughout the remaining portion of the particular welding operation in which said failure occurs. However, during the next welding operation, the system can operate in its normal way unless a serious defect exists in either one of the two are tubes, in which case the system cannot be restarted. This operation, therefore, accomplishes all of the protective features which are desirable in a system of this nature.

Of course it is to be understood that this invention is not limited to the particular details as described above, as many equivalents will suggest themselves to those skilled in the art. For example, some aspects of this invention may be applied to tubes having other types of igniting Also instead of the rectifiers 26 andnecting an alternating potential between sald cathode and anode, an igniting transformer having an energizing winding energized from the voltage across said are discharge device, a rectifier in series with said winding, a circuit including a rectifier connected across said winding, and an output circuit from said transformer for supplying igniting impulses to said igniting electrode.

2. In combination, a load circuit, circuit means for connecting said load circuit to a source of alternating current, a pair of inversely-connected arc discharge devices interposed in said circuit means for controlling the flow of current to said load circuit, each of said are discharge devices comprising an anode, a pool type are cathode, and

ill,

each df said are discharge devices, each of said transformers having an energizing winding ener gized from the voltage acrosssaid tube, a rectifier in series with each of said windings, and an output circuit from each of said transformers for supplying igniting impulses to one of said igniting electrodes.

3. In combination, a load circuit, circuit means for connecting said load circuit to a source or al= ternating current, a pair of inversely-connected arc discharge devices interposed in said circuit means for controlling the flow of current to said load circuit, each of said are discharge devices comprising an anode, a pool type arc cathode, and

an igniting electrode adapted to initiate an arc spot on said cathode, an igniting transformer for each of said arc discharge devices, each of said transformers having an energizing winding energized from the voltage across said tube, a rec tiiier in series with each of said windings, each of said rectifiers being connected in parallel with the winding in series with the other of said rec tirlers, and an output circuit from each of said transformers for supplying igniting impulses to one of said igniting electrodes.

4. In combination, an arc discharge device comprising an anode, a pool type are cathode, and an igniting electrode separated from said cathode by an insulating wall, circuit means for con necting an alternating potential between said cathode and anode, an igniting transformer having an energizing winding energized from the voltage across said tube, a rectifier in series with said winding, a circuit including a rectifier connected across said winding, and an output circult from said transformer for supplying igniting impulses to said igniting electrode.

5. In combination, a load circuit, circuit means for connecting said load circuit to a source of alternating current, a pair of inversely-connected arc discharge devices interposed in said circuit means for controlling the flow of current to said load circuit, each of said are discharge devices comprising an anode, a pool type are cathode, and an igniting electrode separated from said cathode by an insulating wall, an igniting transformer for each of said are discharge devices,

each of said transformers having an energizing winding energized from the voltage across said tuhe, a rectifier in series with each of said windings, and an output circuit from each of said transformers for supplying igniting impulses to one of said igniting electrodes.

6. In combination, a load circuit, circuit means for connecting said load circuit to a source of al ternating current, a pair of inversely-connected arc discharge devices interposed in said circuit means ior controlling the flow of current to said load circuit, each of said arc discharge devices comprising an anode, a pool type are cathode, and an igniting electrode separated from said cathode by an insulating wall, an igniting transformer for each of said are discharge devices, each of said transformers having an energizing winding energized from the voltage across said tube, a rectifier in series with each of said windings, each or said rectifie rs being connected in parallel with the winding in series with the other of said rectifiers, and an output circuit from each of said transformers for supplying igniting impulses to one of said igniting electrodes.

"1. In combination, an arc discharge device comprising an anode, a pool type arc cathode, and

accuses an igniting electrode adapted to initiate an are spot on said cathode, circuit means for connecting an alternating potential between said cathode and anode, an igniting transformer having an energizing winding energized from the voltage across said tube, a rectifier in series with said winding, a circuit including a rectifier connected across said winding, an output circuit from said transformer for supplying igniting impulses to said igniting electrode, and control means for controlling the connection of said winding to the energizing voltage.

ii. In combination, a load circuit, circuit means for connecting said load circuit to a source of alternating current, a pair of inversely-connected arc discharge devices interposed in said circuit means for controlling the flow of current to said load circuit, each of said arc discharge devices comprising an anode, a pool type are cathode, and an igniting electrode adapted to initiate an are spot on said cathode, an igniting transformer for each. of said are discharge devices, each of said transformers having an energizing winding energized from the voltage across said tube, a rectirler in series with each of said windings, an output circuit from each of. said transformers for supplying igniting impulses to one of said igniting electrodes, and control means for controlling the connection of said winding to the energizing voltage.

9. In combination, a load circuit, circuit means for connecting said load circuit to a source of alternating current, a'pair of inversely-connected arc discharge devices interposed in said circuit means for controlling the flow of current to said load circuit, each of said are discharge devices comprising an anode, a pool type arc cathode, and an igniting electrode adapted to initiate an are spot on said cathode, an igniting transformer for each of said are discharge devices, each of said transformers having an energizing winding energized from the voltage across said tube, a rectifier in series with each of said windings, each of said rectifiers heing connected in parallel with the winding in series with the other of said rectifiers, an output circuit from each or" said transformers for supplying igniting impulses to one of said igniting electrodes, and control means for controlling the connection of said winding to the energizing voltage.

10. In combination, a load circuit, circuit means for connecting said load circuit to source of alternating current, a pair of inversely-connected arc discharge devices interposed in said circuit means for controlling the flow of current to said load circuit, each of said are discharge devices comprising an anode, a pool type are cathode, and an igniting electrode separated from said cathode by an insulating wall, an igniting transformer for each of said are discharge devices, each oi said transformers having an energizing winding energized from the voltage across said tube, a rectifier in series with each of said windings, each of said rectifiers being connected in parallel with the winding in series with the other of said rectifiers, an output circuit from each of said transformers for supplying igniting impulses to one of said igniting electrodes, and control means for controlling the connection of said winding to the energizing voltage.

ll. In combination, a load circuit having a power factor less than unity, circuit means for connecting said load circuit to a source of alternating current, a pair of inversely-connected arc discharge devices interposed in said circuit means aeoneee an igniting electrode separated from said cathode v by an insulating wall, an igniting circuit for supplying each oi. said igniting electrodes with ignit-,

ing impulses, and means for energizing said igniting circuits from across said are discharge devices, whereby the voltage impulses occurring across said are discharge devices constitute said igniting impulses.

12. In combination, a load circuit, circuit means for connecting said load circuit to a source of alternating current, a pair of inversely-connected arc discharge devices interposed in said circuit means for controlling the iiow of current to said load circuit, each of said arc discharge devices comprising an anode, a pool type arc cathode, and an igniting electrode adapted to initiate an are spot on said cathode, an igniting circuit for supplying each of said igniting electrodes with igniting impulses, means for energizing said igniting circuits from across said are discharge devices, whereby the voltageimpulses occurring across said are discharge devices constitute said igniting impulses, and means responsive to the voltage across said are discharge devices for deenergizing said igniting circuits when either of said arc discharge devices fails to fire and for maintaining said igniting circuits deenergized.

13. In combination, a load circuit, circuit means for connecting said load circuit to a source of alternating current, a pair oi! inversely-connected arc discharge devices interposed in said circuit means for controlling the flow of current to said load circuit, each of said are discharge devices comprising an anode, a pool type are cathode, and an igniting electrode adapted to initiate an arc spot on said cathode, an igniting circuit for supplying each of said igniting electrodes with igniting impulses, means for energizing said igniting circuits from across said arc discharge devices, whereby the voltage impulses occurring across said are discharge devices constitute said igniting impulses, and means responsive to the occurrence of a voltage impulse of substantially longer duration than a normal igniting impulse for deenergizing said igniting circuits and for maintaining said igniting circuits deenergized.

14. In combination, a load circuit, circuit means for connecting said load circuit to a source of alternating current, a pair of inversely-connected arc discharge devices interposed in said circuit means for controlling the flow of current to said load circuit, each of said are discharge devices comprising an anode, a pool type are cathode, and an igniting electrode adapted to initiate an are spot on said cathode, an igniting circuit for supplying each of said igniting electrodes with igniting impulses, means for energizing said igniting circuits from across said are discharge devices, whereby the voltage impulses occurring across said are discharge devices constitute said igniting impulses, means responsive to the voltage across said are discharge devices for deenergizing said igniting circuits when either of said arc discharge devices fails to fire and for maintaining said igniting circuits deenergized, and independent means for deenergizing said voltage-responsive means to reinitiate the operation of the system.

15. In combination, a load circuit, circuit means for connecting said load circuit to a source of alternating current, a pair of inversely-connected arc discharge devices interposed in said circuit means for controlling the iiow of current to said load circuit, each of said are discharge devices comprising an anode,a pool type arc cathode, and an igniting electrode adapted to initiate an are spot on said cathode, an igniting circuit for supplying each of said igniting electrodes with igniting impulses, means for energizing said igniting circuits from across said are discharge devices, whereby the voltage impulses occurring across said are discharge devices constitute said igniting impulses, a relay having operating means coupled across said are discharge devices responsive to theoccurrence of a voltage impulse of substantially longer duration than a normal igniting impulse, and circuitinterrupting means operated by said relay for deenergizing said igniting circuits upon the occurrence of such a long voltage impulse and for maintaining said igniting circuits deenergized.

16. In combination, a load circuit, circuit means for connecting said load circuit to a source of alternating current, a pair of inversely-connected arc discharge devices interposed in said circuit means for controlling the flow of current to said load circuit, each of said arc discharge devices comprising an anode, a pool type are cathode, and an igniting electrode adapted to initiate anarc spot on said cathode, an igniting circuit for supplying each of said igniting electrodes with igniting impulses, means for energizing said igniting circuits from across said arc discharge devices, whereby the voltage impulses occurring across said are discharge devices constitute said igniting impulses, means responsive to the voltage across said are discharge devices for deenergizing said igniting circuits when either of said are discharge devices fails to fire, and circuit-closing means interposed between said voltage across said are discharge devices and said igniting circuits and said voltage-responsive means, whereby said voltage-responsive means, when operated, maintains said igniting circuits deenergized until said circuit-closing means is opened.

1'7. In combination, "a load circuit, circuit means for connecting said load circuit to a source of alternating current, a pair of inversely-connected arc discharge devices interposed in said circuit means for controlling the flow of current to said load circuit, each of said arc discharge devices comprising an anode, a pool type arc cath ode, and an igniting electrode adapted to initiate an are spot on said cathode, an igniting circuit for supplying each of said igniting electrodes with igniting impulses, means for energizing said igniting circuits from across saidv are discharge devices, whereby the voltage impulses occurring across said are discharge devices constitute said igniting impulses, a relay having operating means coupled across said are discharge devices responsive to the occurrence of a voltage impulse of substantially longer duration than a normal igniting impulse, circuit-interrupting means operated by said relay for deenergizing said igniting circuits upon the occurrence of such a long voltage impulse, and circuit-closing means interposed between said voltage across said arc discharge devices and said igniting circuits and said operating means, whereby said operating means, when operated, maintains said igniting circuits denergized until said circuit-closing means is opened.

18. In combination, a load circuit, circuit means for connecting said load circuit to a source of alternating current, a pair of inversely-connected arc discharge devices interposed in said circuit means for controlling the flow of ourcharge devices comprising an anode. a pool type are cathode, and an igniting electrode separated! from said cathode by an immunizing wall, an ignifiing circuit ficr cuppiyiug ewh of said igniting electrodes with igniting impulscc, and means for 9,201,906 rent c said 1M circuit, each of said we disencrgizing said igniting circuits from cc 'osc said are discharge devices, whereby the voltage impulses occurring acrcsccaid arc discharge devices ccnstit-utc said igniting impulses.

JUN W. DAWSON. 

